Hard Reality, Water Condition and Chemical Performance

Assess the condition of local water to ensure chemical performance

In many areas of the country, hard water is a fact of life. With a growing number of farmers owning self-propelled sprayers, it’s a good idea to re-evaluate best practices to ensure chemical performance, particularly for glyphosate applications, explains Bob Hartzler, Iowa State University Extension weed scientist.

"Most water sources have various salts and cations, and some of those will form complexes with the glyphosate that greatly reduce the glyphosate’s activities," Hartzler says.

With numerous water-softening products on the market, it’s hard to know which ones work, says Fred Whitford, coordinator of the Purdue University pesticide programs.

When evaluating water-softening products, Whitford says, consider the following tips:

There are no regulatory standards for such products, so you need to trust the seller.

The major players who produce these adjuvants have chemists on staff. They know what compounds they can use to tie up the calcium and magnesium. In all likelihood, this array of products works in similar ways.

Determine whether the pesticide in question is impacted by hard water.

Determine the hardness of the water being used for application.

Don’t forget that inexpensive pH and hardness kits can be helpful.

Know for sure. Farmers should test water to determine local hardness levels. When a softener such as ammonium sulfate is needed, the standard rate isn’t always required, Hartzler says. For example, some studies have found that while the standard usage rate for ammonium sulfate in Iowa is 17 lb. per 100 gal. of water, 90% of the state’s water sources are soft enough that farmers can get by with less than half that amount.

Anecdotal evidence suggests that using ammonium sulfate to fix hard water has benefits during a glyphosate application. "Seldom do I hear that it increased yields," Whitford says. "What I hear is that the product was hotter, the weeds died quicker, even some that were difficult to knock down."

While those benefits are easy to spot in the field, the challenge is identifying which product will prevent potassium ions attached to glyphosate from being replaced by negative metal ions such as magnesium and iron, reducing the effectiveness of the herbicide, Hartzler says. While ammonium sulfate is the most popular, it doesn’t always dissolve well in very cold water, and it can plug up sprayer nozzles. At the same time, a common alternative—water conditioners—might not contain enough ammonium to reduce water hardness.

It’s important to read product labels, know the active ingredients and verify whether the product was designed for use with herbicides, Hartzler says.

"We realize that from the time we put the chemical in the tank, to the time it comes out of the nozzle, to the time it hits the plant, there are all kinds of things that we call fail factors," Whitford says. "These factors can reduce the efficacy of the product if we don’t overcome them."